The present invention pertains generally to the processing of RF and/or microwave signals, and more particularly, to the detection and geolocation of the source of low-power, broadband, poorly-coherent amplitude-modulated RF signals.
Detecting and geolocating sources of RF signals are vital requirements of intelligence, surveillance, and reconnaissance activities within the military and law enforcement communities. The present invention markedly improves the capability to sense and accurately locate low-power, broadband, amplitude-modulated RF or microwave signals having poor coherency.
The invention relates to methods and systems to detect low-power, broadband, amplitude-modulated signals. The signals may be RF or microwave. The invention also concerns methods and systems for analyzing such a detected signal in order to geolocate the source of the signal. By demodulating and analyzing the low frequency amplitude modulations (for example, in the 30 Hz-10,000 Hz range) which are superimposed on high frequency carrier signals (for example, in the 100 MHz-10 GHz), the present invention may reveal further information regarding the identification of the emitter type.
Systems for analyzing an amplitude-modulated signal are disclosed. According to one embodiment of the present invention, the system includes an antenna array, a RF subsystem, and a computational subsystem. The antenna array generates at least two antenna beams and an output signal for each of the at least two antenna beams. The RF subsystem processes the outputs for each of the at least two antenna beams and produces at least two channel outputs. The computational subsystem includes a detector that detects amplitude modulations that may be superimposed on the amplitude-modulated signal, an analog-to-digital converter that generates digital output data, and a digital signal processing unit that analyzes the digital output data to characterize a source of the amplitude-modulated signal.
Systems for analyzing an RF/microwave signal are disclosed. According to one embodiment of the present invention, the system includes an antenna assembly, a receiver, at least one crystal detector, an analog to digital converter, and a processor. The antenna assembly generates at least two antenna beams, each of the antenna beams generating an output signal. The receiver receives the output signals from the antenna assembly. The crystal detector detects amplitude modulations that may be present on the RF/microwave signal. The analog to digital converter converts the detected amplitude modulations to digital data. The processor processes the digital data to determine directional information for a source of the RF/microwave signal.
In another embodiment a single conversion receiver is used having a peak detector instead of a diode-detector TRF system.
A radio direction finder system for determining location information for a source of an RF/microwave signal is disclosed. According to one embodiment of the present invention, the radio direction finder system includes an antenna assembly, a first receiver, a second receiver, a first AM detector, a second AM detector, and a processor.
The antenna assembly generates a first and a second antenna beam, and the first and second antenna beams generating a first and second RF output signal, respectively. The first receiver receives the first RF output signal. The second receiver receives the second RF output signal. The first AM detector extracts amplitude variations from the first RF output signal and generates a first detected signal. The second AM detector extracts amplitude variations from the second RF output signal and generates a second detected signal. The processor determines directional information from the first and second detected signals.
A system for analyzing an RF/microwave signal is disclosed. According to one embodiment of the present invention, the system includes an antenna assembly, a receiver, at least one crystal detector, an analog to digital converter, and a processor.
The antenna assembly generates at least two antenna beams, each of the antenna beams generating an RF output signal. The receiver receives the RF output signals from the antenna assembly. The crystal detector detects amplitude modulations that may be present on the RF/microwave signal. The analog to digital converter converts the detected amplitude modulations to digital data. The processor processes the digital data to determine information about a source of the RF/microwave signal.
A method for characterizing a source of an RF signal having amplitude modulations is disclosed. According to one embodiment of the present invention, the method includes the steps of (1) receiving an RF signal; (2) filtering the RF signal; (3) amplifying the filtered signal; (4) detecting amplitude modulations from the filtered signal; (5) converting the amplitude modulations into digital data; and (6) processing the digital data to characterize a source of the RF signal.
A method for analyzing a source of an RF/microwave signal having amplitude modulations is disclosed, which method includes: providing a first antenna beam from a phased antenna array, the first antenna beam having a first beam width; providing a second antenna beam from a second phased antenna array, the second antenna beam having a second beam width and being offset from the first antenna beam by a squint angle, said first antenna beam overlapping at least partially with said second antenna beam; searching for an RF signal by manipulating the first and second beams; and detecting amplitude modulations from the RF signal; converting the amplitude modulations using an analog to digital converter to generate digital data; and analyzing the digital data to geolocate the source of the RF signal. The method may use diode detectors to detect the amplitude modulations.
A system for geolocating a source of an RF/microwave signal is also enclosed that involves the use of two detection systems. The first detection system includes: an antenna assembly that generates at least two antenna beams, each of said at least two antenna beams generating an output signal; a receiver for each of the at least two antenna beams to receive the output signals from the antenna assembly; at least one crystal detector for each output signal, each crystal detector detecting amplitude modulations that may be present on the RF signal; an analog to digital converter to convert the detected amplitude modulations to digital data; and a processor that processes the digital data to determine a first angular location of the source of the RF signal relative to the first detection system. The second detection system includes: an antenna assembly that generates at least two antenna beams, each of said at least two antenna beams generating an output signal; a receiver for each of the at least two antenna beams to receive the output signals from the antenna assembly; at least one crystal detector for each output signal, each crystal detector detecting amplitude modulations that may be present on the RF signal; an analog to digital converter to convert the detected amplitude modulations to digital data; and a processor that processes the digital data to determine a second angular location of the source of the RF signal relative to the second detection system. The first detection system is spaced apart from the second detection system such that the range of the source of the RF signal can be determined using the first angular location, the second angular location, the location of the first detection system, and the location of the second detection system.
A method for geolocating a source of an RF or microwave signal having amplitude modulations is disclosed, which method includes the use of two antenna assemblies. With reference to the first antenna assembly, the steps include: locating a first antenna assembly at a known location relative to a second antenna assembly; receiving the RF signal using the first antenna assembly and generating a first output signal; detecting amplitude modulations from the first output signal; converting the amplitude modulations into digital data; and processing the digital data to determine an angular location of the source of the RF signal relative to first antenna assembly. With reference to the second antenna assembly, the steps include: receiving the RF signal using the second antenna assembly and generating a second output signal; detecting amplitude modulations from the second output signal; converting the amplitude modulations into digital data; and processing the digital data to determine an angular location of the source of the RF signal relative to second antenna assembly. Thereafter, the range and location of the source of the RF signal can be determined using the first angular location, the second angular location, and the relative locations of the first antenna assembly and the second antenna assembly.
Also disclosed is a system for analyzing an RF/microwave signal, comprising an antenna assembly that generates at least one antenna beam and that generates a left RF output signal; an antenna assembly that generates at least one antenna beam and that generates a right RF output signal; a first RF splitter that splits the left RF output signal into a first component left RF signal and a second component left RF signal; a second RF splitter that splits the right RF output signal into a first component right RF signal and a second component right RF signal; a first RF phase shifter to shift the phase of the first component left RF signal; a second RF phase shifter to shift the phase of the second component right RF signal; a first RF combiner to combine the second component left RF signal with the phase-shifted second component right RF signal to create a second channel output; a second RF combiner to combine the first component right RF signal with the phase-shifted first component left RF signal to create a first channel output; a first receiver to receive the first channel output signal, wherein the first receiver comprises: at least one crystal detector to detect amplitude modulations that may be present on the first channel output signal; and an analog to digital converter to convert the detected amplitude modulations to first channel digital data; a second receiver to receive the second channel output signal, wherein the second receiver comprises: at least one crystal detector to detect amplitude modulations that may be present on the second channel output signal; and an analog to digital converter to convert the detected amplitude modulations to second channel digital data; and a digital signal processor that processes the first channel digital data and the second channel digital data to determine information about a source of the RF/microwave signal. In a desirable embodiment the digital signal processor utilizes FFT algorithms to analyze the first channel digital data and the second channel digital data to determine location information about a source of the RF/microwave signal. In yet another desirable embodiment the first phase shifter and the second phase shifter shift their input signals by approximately equal and opposite phase angles. Most desirably one phase shifter operate at +60 degrees and the other operates at xe2x88x9260 degrees.